Fan modules and server equipment

ABSTRACT

A fan module and server equipment are provided that can achieve a balance between increased airflow and noise reduction when an axial flow fan is mounted in the server equipment. 
     The fan module for taking in and discharging air includes a stator located on an upstream side with respect to airflow and an axial flow fan located on the downstream side. When the fan module is viewed from the rotational-axial direction of the axial flow fan, if a leading edge of a rotor vane constituting part of the axial flow fan passes a trailing edge of a stator vane constituting part of the rotor, a skew is formed in which the leading edge of the rotor vane constantly intersects the leading edge of the rotor vane at a single point.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to fan modules and serverequipment. The invention more particularly relates to a fan moduleformed by combining an axial flow fan with a stator, and serverequipment which is an information instrument in which the fan module ismounted.

2. Description of the Related Art

Office automation equipment, IT devices and home electric appliancesinclude therein a cooling fan for cooling electronic components fromwhich heat is emitted. In recent years, these home electric appliances,office automation equipment and home electric appliances haveincreasingly been downsized and sophisticated in the market. Electroniccomponents in the internal structure of the equipment or the like areincreased in density along with the downsizing and sophistication. Thus,the amount of heat generation across the electronic components tends toincrease.

To address the increase in the heat generation across the electroniccomponents, an axial flow fan that is small-sized and can easily provideairflow is generally employed as a cooling fan. In many cases, designersuse general-purpose axial flow fans available from fan's vendors toimplement such small-sized axial flow fans in the equipment in a mannersuitable for their respective applications.

Naturally, each of the general-purpose small-sized axial flow fans isnot adjusted to match a corresponding one of devices. Therefore, manydevices cannot bring out desired performance from the axial flow fans.

In particular, when boards and the like are mounted in high density in adevice such as information instruments represented by server equipmentused in a data center, airflow entering the axial flow fan is madeturbulent and flow passages for such airflow are reduced in width. Thus,an amount of airflow generated by the axial flow fan is significantlylowered and noise is increased.

Accordingly, general-purpose small-sized axial flow fans to be mountedin information instruments emphasize technologies for enabling increasedairflow and reduced noise.

For example, WO2008/062835 describes the following. A first axial flowfan and a second axial flow fan, i.e., two axial flow fans in total, arearranged in series in the order from the upstream side of airflow withrespect to a rotational-axial direction of the fan. A flow straighteneris disposed between the first and second axial flow fans. The flowstraightener changes the direction of airflow coming out from the firstaxial flow fan, thereby applying a swirl flow in a direction reverse tothe rotational direction of the second axial flow fan to the secondaxial flow fan. There is an effect of improving the static pressurecharacteristics of the two axial flow fans to increase the amount ofairflow.

SUMMARY OF THE INVENTION

The conventional technology as mentioned above produces the effect ofimproving the amount of airflow; however, it does not refer to noisereduction. Therefore, there is the necessity of achieving a balancebetween the increase in airflow and the noise reduction when the axialflow fans are mounted. In addition, since the conventional technologypremises the series configuration of the two axial flow fans, there is aproblem in that the conventional technology cannot be applied toinformation instruments that do not meet such a premise.

It is an object of the present invention to provide a fan module andserver equipment that achieve increased airflow and reduced noise of anaxial flow fan to be mounted on an information instrument or the like.

According to an aspect of the present invention, there is provided a fanmodule for taking in and discharging air, including: a stator located onan upstream side with respect to airflow; and an axial flow fan locatedon a downstream side with respect to the airflow. When the fan module isviewed from a rotational-axial direction of the axial flow fan, thestator includes a stator vane trailing edge and the axial flow fanincludes a rotor vane leading edge, the trailing edge and the leadingedge each having two points of intersection with two concentric circleshaving different diameters. A straight line connecting the two points ofintersection on the trailing edge and a straight line connecting the twopoints of intersection on the leading edge are configured such that if,on one of the two concentric circles, one point of intersection on thetrailing edge is superimposed on the point of intersection on theleading edge, on the other of the two concentric circles, the otherpoint of intersection on the trailing edge is not coincident with theother point of intersection on the leading edge.

Preferably, the rotor vane has a tilt direction opposite to that of thestator vane.

Preferably, the stator vane applies a reverse pre-swirl to the rotorvane.

Preferably, the stator vane constituting part of the stator isconfigured to be warped like a U-shape.

Preferably, a second stator is disposed on the downstream side of theaxial flow fan.

Preferably, a trailing edge of a stator vane constituting part of thesecond stator disposed on the downstream side of the axial flow fan islocated at a positive position with respect to a position of a leadingedge of the stator vane in a rotational direction of the axial flow fan.

Preferably, an interval between adjacent stator vanes constituting partof the stator is smaller than a width of a finger.

Preferably, the axial flow fan and the stator constituting the fanmodule are integrated with each other.

Preferably, a plurality of the fan modules are combined in series or inparallel.

According to another aspect of the present invention, there is providedserver equipment in which the fan module described above is mounted.

The present invention can provide a fan module that can achieve abalance between increased airflow and noise reduction in an axial flowfan mounted in server equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a fan module according to a firstembodiment of the present invention.

FIG. 2 is a perspective view of a stator constituting part of the fanmodule shown in FIG. 1.

FIG. 3 is a perspective view of an axial flow fan constituting part ofthe fan module shown in FIG. 1.

FIG. 4 is an explanatory view showing a state of airflow entering theaxial flow fan exposed to the atmosphere.

FIG. 5 is an explanatory view showing a state of airflow entering theaxial flow fan mounted in an information instrument.

FIG. 6 is a graph showing a comparison of velocity distribution ofairflow entering the axial flow fan between when the axial flow fan isexposed to the atmosphere and when it is mounted in the informationinstrument.

FIG. 7 is a diagram partially showing the fan module shown in FIG. 1 asviewed from a direction of a rotational axis.

FIG. 8 is a graph showing an effect of a second embodiment of thepresent invention.

FIG. 9 is a schematic cross-sectional view of a fan module according toa third embodiment of the present invention.

FIG. 10 is a perspective view of a fan module according to a fourthembodiment of the present invention.

FIG. 11 is a perspective view of a stator constituting part of the fanmodule shown in FIG. 10.

FIG. 12 is a schematic cross-sectional view of the fan module accordingto the fourth embodiment of the present invention.

FIG. 13 is a perspective view of a fan module according to a fifthembodiment of the present invention.

FIG. 14 is a perspective view of a stator constituting part of the fanmodule shown in FIG. 13.

FIG. 15 is a configurational schematic of a PC server according to asixth embodiment of the present invention.

FIG. 16 is a perspective view of a fan module according to a seventhembodiment of the present invention.

FIG. 17 is a graph showing an effect of the seventh embodiment of thepresent invention.

FIG. 18 is a perspective view of a fan module according to an eighthembodiment of the present invention.

FIG. 19 is a perspective view of a fan module according to a ninthembodiment of the present invention.

FIG. 20 is a configurational schematic of a blade server according to atenth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present embodiment will hereinafter bedescribed with reference to the drawings. A schematic configuration of afan module is first described with reference to FIGS. 1 to 3. Membersdenoted with the same reference numerals in the figures have the samefunction; therefore, their explanations may be omitted in other figures.FIG. 1 is a perspective view of a fan module. The fan module 1 isconfigured such that a stator 2 and an axial flow fan 3 are arranged inseries in this order from the upstream side of airflow.

FIG. 2 is a perspective view of the axial flow fan 2. The axial flow fan2 includes a boss 21, stator vanes 22 extending from the boss 21, and anouter frame 23 supporting the stator vanes.

FIG. 3 is a perspective view of the axial flow fan. The axial flow fan 3includes a rotating boss 31 to which a motor is mounted; rotor vanes 32extending from the boss 31; a motor cup 33 supporting the motor mountedto the boss; braces 34 supporting the motor cup 33; and an outer frame35 supporting the braces 34.

First Embodiment

A first embodiment is described with reference to FIGS. 4, 5 and 6. FIG.4 is an explanatory view showing a state of airflow entering the axialflow fan exposed to the atmosphere. FIG. 5 is an explanatory viewshowing a state of airflow entering the axial flow fan mounted in aninformation instrument. FIG. 6 is a graph showing a comparison invelocity distribution of airflow entering the axial flow fan betweenwhen the axial flow fan is exposed to the atmosphere and when it ismounted in the information instrument.

In cooling a variety of information instruments, resistor bodies such asboards which disturb airflow are generally located on the upstream sideof a cooling fan. If the airflow thus disturbed by these resistor bodiesenters the cooling fan mounted in an information instrument, noises aregenerated. As shown in FIG. 4, general-purpose small-sized axial flowfans are presupposed to be used under atmosphere-exposure conditions;therefore, they are designed under the assumption that airflow a1 entersthe axial flow fan not only from a rotational-axial direction but from adirection perpendicular to the rotational-axial direction. On the otherhand, the axial flow fan mounted in the information instrument has arestricted flow passage; therefore, airflow a2 enters the axial flow fanonly from the rotational-axial direction as shown in e.g. FIG. 5. Ifdistributions in airflow velocity in the rotational-axial direction arecompared between the conditions of airflow into the axial flow fan asdescribed above, the results are as shown in FIG. 6. In FIG. 6, anintersection between a vertical axis and a transverse axis correspondsto the position of radius 0 of the axial flow fan (i.e., the position ofthe center of the axial flow fan). As seen from FIG. 6, in the case ofthe axial flow fan mounted in the information instrument (the solid linein FIG. 6), the velocity of airflow in a rotational-axial direction isaveragely increased because of the restricted flow passage. In otherwords, the average value of the velocity distribution of airflowentering the axial flow fan mounted in the information instrument isgreater than that of the airflow entering the axial flow fan exposed tothe atmosphere.

The axial flow fan mounted in the information instrument is used underthe conditions different from originally assumed conditions. Therefore,an amount of airflow and static pressure are reduced.

If the fan module 1 shown in FIG. 1 is used to cool a variety ofinformation instruments similarly to the conventionally used axial flowfan, airflow disturbed by the resistor bodies (specific examples aredescribed later but they mean objects to be cooled in e.g. serverequipment) located on the upstream side of the fan module isstraightened by the stator 2. Thereafter, the airflow thus straightenedenters the axial flow fan 3. In this way, disturbed airflow does notenter the axial flow fan 3. Thus, possible noise can be suppressed. Evenin the state where the axial flow fan is mounted in the informationinstrument, the axial flow fan is improved to meet the inflow conditionsassumed when designing the axial flow fan. Thus, the amount of airflowand static pressure of the axial flow fan mounted in the informationinstrument are increased compared with an axial flow fan not providedwith a stator on the upstream side thereof.

Second Embodiment

As shown in FIG. 1, the fan module 1 has the stator 2 disposedimmediately in front of the axial flow fan 3. The rotor vanes 32 arerotated along with the rotation of the boss 31 to which the motor of theaxial flow fan 3 is attached. The rotation of the rotor vanes 32 causesinterference with the stator vanes 22 of the stator. Thus, there isconcern about increased noise of frequencies resulting from the numberof the rotor vanes 32 or of the stator vanes 22.

To address the concern noise, a second embodiment focuses on apositional relationship between the stator vanes 22 and the rotor vanes32. This suppresses increase in the noise of frequencies resulting fromthe number of the rotor vanes 32 or the stator vanes 22.

FIG. 7 partially shows the fan module 1 as viewed from the upstream sideof airflow in the rotational-axial direction of the rotor vanes 32. Asdescribed earlier, the interference between the rotor vanes 32 and thestator vanes 22 occurs when the rotor vane 32 rotating in the directionof an arrow in FIG. 7 passes the stator vane 22 at rest.

In FIG. 7, circles 41, 42 have different radii and are concentric withthe boss 21 of the stator 2. A point of intersection between the circle41 and the stator vane 22 is assumed as a point 43. A point ofintersection between the circle 42 and the stator vane 22 is assumed asa point 44. A point of intersection between the circle 41 and the rotorvane 32 is assumed as a point 45. A point of intersection between thecircle 42 and the rotor vane 32 is assumed as a point 46. A line segmentconnecting the point 43 with the point 44 is assumed as a line 47, and aline segment connecting the point 45 with the point 46 is assume as aline 48. The fan module in the second embodiment is configured such thatif the point 43 and the point 45 are superimposed on each other on thecircle 41 or the point 44 and the point 46 are superimposed on eachother on the circle 42, the line 47 is not coincident with the line 48.This non-coincident configuration means a state where as shown in e.g.FIG. 7, if the point 46 on the rotor vane 32 shifts to a positionsuperimposed on the point 44 on the stator vane, another point 45′ onthe rotor vane 32 is not superimposed on the point 43 on the statorvane.

More specifically, the fan module taking in and discharging air ischaracteristically configured as below. The fan module includes thestator located on the upstream side with respect to airflow and theaxial flow fan located on the downstream side. When the fan module isviewed from the rotational-axial direction of the axial flow fan, if twovirtual concentric circles having different radii are assumed, atrailing edge of a stator vane constituting part of the stator and aleading edge of a rotor vane constituting part of the axial flow faneach have two points of intersections with the two concentric circles. Astraight line connecting the two points of intersection on the trailingedge of the stator vane and a straight line connecting the two points ofintersection on the leading edge of the rotor vane are configured asbelow. If, on one of the two concentric circles, one point ofintersection on the trailing edge of the stator vane is superimposed onthe point of intersection on the leading edge of the rotor vane, on theother of the two concentric circles, the other point of intersection onthe trailing edge of the stator vane is not coincident with the otherpoint of intersection on the leading edge of the rotor vane.

Further, when the leading edge of the rotor vane passes the trailingedge of the stator vane, a skew is formed in which the leading edge ofthe rotor vane constantly intersects the leading edge of the rotor vaneat a single point.

With this configuration, the rotor vane 32 constantly passes the statorvane 22 only at a single point. Therefore, an area where theinterference between the rotor vane and the stator vane occurssimultaneously can be minimized. This can produce an effect ofsuppressing an increase in the sound pressure level of each frequencycomponent of noises resulting from the number of the rotor vanes 32 orthe stator vanes 22. FIG. 8 is a graph showing the effect of the secondembodiment. FIG. 8 can confirm the fact that the fan module of thesecond embodiment shown in FIG. 7 can reduce the noise of vane passingfrequency (the sound pressure level) resulting from the number of therotor vanes or the stator vanes. If the second embodiment isimplemented, the sound pressure level is lowered as a whole comparedwith the case that the second embodiment is not implemented.Incidentally, if “order of vane passing frequency” of the horizontalaxis in FIG. 8 is n-order, a relationship is such that “noisefrequency”/(“the rotation number of the axial flow fan”×“the number ofvanes”)=n.

Third Embodiment

In a third embodiment, a configuration in which the direction of airflowis changed by stator vanes is added to that of the first or secondembodiment to thereby increase the amount of airflow in a fan modulemounted in server equipment such as an information instrument. FIG. 9 isa schematic cross-sectional view of a fan module of the thirdembodiment, showing a positional relationship between a stator vane 22and a rotor vane 32. The stator vane 22 of a stator and the rotor vane32 of an axial flow fan are arranged from the upstream side of airflow.The rotor vane 32 is rotated in a rotational direction R. The statorvane 22 is warped in a U-shape in cross-section relative to therotational direction R.

A velocity component 51 of airflow entering the fan module is changed indirection by the stator vane 22 and turned to a velocity component 52 ofthe airflow, which enters the rotor vane 32. In other words, because ofthe presence of the stator vane 22, the airflow having a velocitycomponent 54 which is a circumferential velocity in a direction reverseto the rotational direction R enters the rotor vane 32. In short, thestator vane applies a reverse pre-swirl to the rotor vane. In general,an axial flow fan is designed under the assumption that the airflowentering the rotor vane has no circumferential velocity component.However, if the axial flow fan is mounted in a variety of informationinstruments or the like for use, airflow is disturbed; therefore, theairflow having a circumferential velocity component which has the samedirection as the rotational direction of the axial flow fan enters theaxial flow fan. Incidentally, a velocity component 53 of the airflow hasthe same direction and magnitude as those of the velocity component 51of airflow entering the fan module.

[Expression 1]

P _(th)=ρ(C _(u2) u ₂ −C _(u1) u ₁)  expression 1

P_(th): Theoretical total pressure

ρ: Density

C_(u1): Swirl velocity at rotor vane inlet

C_(u2): Swirl velocity at rotor vane outlet

u₁: Circumferential velocity at rotor vane inlet

u₂: Circumferential velocity at rotor vane outlet

Expression 1 is an expression representing the theoretical totalpressure of the axial flow fan. According to this expression, thetheoretical total pressure of the axial flow fan is obtained bymultiplying a value by the air density ρ, such a value being obtained byreducing the product of the swirl velocity C_(u1) which is thecircumferential velocity component at the axial flow fan inlet and therotating velocity u₁ from the product of the swirl velocity C_(u2) whichis the circumferential velocity component at the axial flow fan outletand the rotating velocity u₂. This expression shows that if the airflowentering the axial flow fan has a circumferential velocity component inthe same direction as the rotational direction of the axial flow fan,the total pressure of the axial flow fan is lowered. On the other hand,the stator vane 22 of the third embodiment allows the airflow having thecircumferential velocity component in a direction reverse to therotational direction R of the rotor vane 32 to enter the rotor vane 32.According to expression 1, such airflow increases the theoretical totalpressure of the axial flow fan, which leads to increased static pressureand also to the increased amount of airflow.

Fourth Embodiment

FIG. 10 is a perspective view of a fan module 11 according to a fourthembodiment. The fan module 11 is configured such that a first stator 2,an axial flow fan 3 and a second stator 6 are arranged in this orderfrom the upstream side of airflow. The first stator 2 and the axial flowfan 3 are the same as those in the first to third embodiments.

FIG. 11 is a perspective view of a configuration of the second stator 6.The second stator 6 includes a boss 61, a plurality of stator vanes 62extending from the boss 61, and an outer frame 63 supporting the statorvanes 62.

FIG. 12 is a schematic cross-sectional view of the fan module, showing apositional relationship among the stator vane 22, the rotor vane 32 andthe stator vane 62 according to the fourth embodiment. The stator vane22 of the first stator, the rotor vane 32 of the axial flow fan and thestator vane 62 of the second stator are arranged from the upstream sideof airflow. The rotor vane 32 is rotated in a rotational direction R.The stator vane 62 has a trailing edge located at a positive positionwith respect to the position of the leading edge in the rotationaldirection R. Incidentally, the airflow entering the stator vane 22 andreaching the rotor vane 32 is the same as that in FIG. 9. Further, theairflow coming out from the rotor vane 32 enters the stator vane 62 at avelocity component 55. The airflow having passed the stator vane 62 isstraightened and runs out at a velocity component 56.

[Expression 2]

P _(s)=ρη_(s)×(V ₂ ² −V ₃ ²)/2  expression 2

P_(s): Static pressure rise

ρ: Density

η_(s): Static pressure efficiency

V₂: Absolute value of velocity at stator vane inlet

V₃: Absolute value of velocity at stator vane outlet

Expression 2 is an expression representing a static pressure rise due tothe second stator. According to this expression, the static pressurerise due to the second stator is obtained by multiplying a value by thedensity ρ of air and static pressure efficiency η_(s), such a valuebeing obtained by subtracting the square of an absolute value V₃ of thevelocity at the stator vane outlet from the square of an absolute valueV₂ of the velocity at the stator vane inlet. If the effect of the secondstator is correlated with FIG. 12, the velocity component 55 is reducedby the stator vane 62 and changed into velocity 56. That is to say, thestatic pressure is raised according to the reduced velocity to increasethe amount of airflow.

Fifth Embodiment

FIG. 13 is a perspective view of a fan module 12 according to a fifthembodiment. The fan module 12 is configured such that a stator 7 and anaxial flow fan 3 are arranged in series in this order from the upstreamside of airflow.

FIG. 14 is a perspective view of a detailed configuration of the stator7 in FIG. 13. The stator 7 includes a boss 71, a plurality of statorvanes 72 extending from the boss 71, one or more guide rings 73, and anouter frame 74 supporting the stator vanes. The number of the statorvanes 72 is set so that the interval between the stator vanes 72adjacent to each other may be smaller than the size of a finger of anoperator handling server equipment. The guide ring or guide rings arefurther installed to completely prevent the entering of the operator'sfinger.

The fan module 12 has an effect of completely preventing the operator'sfinger from entering the stator 7. That is to say, safety measures aretaken for fan module replacing work.

Incidentally, the fifth embodiment does not always need the guide ring73. If the interval between the stator vanes 72 adjacent to each otheris smaller than the size of the operator's finger, the same effect asthat of the guide ring can be produced.

Sixth Embodiment

FIG. 15 is a configurational schematic of a PC server in which fanmodules are mounted according to a sixth embodiment. The PC server 8,which is a type of server equipment, includes a chassis 81, units 82each having an inside board on which a CPU is mounted, and fan modules13.

The fan module described in any one of the first to fifth embodiment canbe used as the fan module 13. The fan module 13 is of an integralstructure in which a stator and an axial flow fan are joined to eachother. Therefore, time required for mounting work and replacing work forthe fan module 13 can be reduced.

Seventh Embodiment

FIG. 16 is a perspective view of a fan module according to a seventhembodiment. A fan module 111 is configured such that a first fan module14 and a second fan module 15 are arranged in series. The fan moduledescribed in any one of the first to sixth embodiments can be used asthe first and second fan modules 14, 15.

Among information instruments, particularly an information instrumenthaving a high-density inside structure is increased in pressure loss.Such an information instrument uses two or more axial flow fans arrangedin series in order to provide an amount of cooling air needed for astatistic pressure rise. The use of the axial flow fans arranged inseries expects to increase the static pressure according to theincreased number of the axial flow fans. However, such an expectedeffect is not generally obtained. For example, if two axial flow fansarranged in series are used, a double static pressure rise is expected.However, only an approximate one-and-a-half static pressure rise can beobtained in actuality.

As in the seventh embodiment, if the fan modules described in any one ofthe first to sixth embodiments are arranged in series for use, thesingle axial flow fan is fan-modularized to increase static pressure andalso airflow is straightened. Thus, as shown in FIG. 17, a staticpressure rise two times or more of that in the case where the singleaxial flow fans are arranged in series can be obtained.

Incidentally, the fan module 111 described in the seventh embodiment isconfigured such that the two fan modules are arranged in series.However, the effect of the seventh embodiment can be produced withoutlimiting the number of the fan modules arranged in series. Additionally,it is not always necessary to use the same fan modules arranged inseries.

Eighth Embodiment

FIG. 18 is a perspective view of a fan module according to an eighthembodiment. A fan module 112 is configured such that a first axial flowfan 3, a first stator 6, a second stator 2 and a second axial flow fan 3are arranged in series in this order from the upstream side of airflow.

When the fan module is viewed from the rotational-axial direction of thesecond axial flow fan, if two virtual concentric circles havingdifferent radii are assumed, a trailing edge of a stator vaneconstituting part of the second stator and a leading edge of a rotorvane constituting part of the second axial flow fan each have two pointsof intersection with the two concentric circles. A straight lineconnecting the two points of intersection on the trailing edge of thestator vane and a straight line connecting the two points ofintersection on the leading edge of the rotor vane are configured asbelow. If, on one of the two concentric circles, one point ofintersection on the trailing edge of the stator vane is superimposed onthe point of intersection on the leading edge of the rotor vane, on theother of the two concentric circles, the other point of intersection onthe trailing edge of the stator vane is not coincident with the otherpoint of intersection on the leading edge of the rotor vane.

Further, the second axial flow fan has the rotor vanes and the secondstator has the stator vanes. It is preferred that the tilt direction ofthe rotor vane be opposite to that of the stator vane.

As with the seventh embodiment, the fan module 112 provides a staticpressure rise greater than that in the case where the axial flow fanunits are arranged in series for use. In particular, if a dimensionallimitation is put on the fan module and the configuration of the seventhembodiment cannot be employed, the present embodiment produces aneffect.

Ninth Embodiment

FIG. 19 is perspective view of a fan module according to a ninthembodiment. A fan module 113 is configured such that a first fan module16 and a second fan module 17 are juxtaposed to each other.

To increase the amount of airflow of, particularly, an informationinstrument having a low-density inside structure among informationinstruments, axial flow fans are juxtaposed to each other for use toincrease the amount of cooling airflow. The use of the fan modulesjuxtaposed to each other as in the present embodiment can increase theamount of airflow for cooling the axial flow fans juxtaposed to eachother and mounted in an information instrument.

Incidentally, the fan module 113 described in the ninth embodiment is afan module in which the two fan modules described in any one of thefirst to eighth embodiments are juxtaposed to each other. However, thefan modules of the present embodiment can produce the effect withoutlimiting the number of the fan modules juxtaposed to one another andwithout the necessity of using the same fan modules.

Tenth Embodiment

FIG. 20 is a configurational schematic of a blade server, which is anexample of server equipment, according to a tenth embodiment. A bladeserver 9 includes a casing 91, an electronic device section 92 includingserver blades, and a fan module 1111.

For example, the fan module 1111 is configured to combine a plurality ofthe fan modules described in any one of the first to ninth embodiments.Therefore, the fan module 1111 produces an effect of increasing theamount of airflow generated by the blade server 9 and of reducing noisethereof.

The application of the fan module in the present embodiment is notlimited to the blade server but can be applied to general serverequipment such as rack servers and PC servers.

It is to be noted that the present invention is not limited to theaforementioned embodiments, but covers various modifications. While, forillustrative purposes, those embodiments have been describedspecifically, the present invention is not necessarily limited to thespecific forms disclosed. Thus, partial replacement is possible betweenthe components of a certain embodiment and the components of another.Likewise, certain components can be added to or removed from theembodiments disclosed.

Note also that some or all of the aforementioned components, functions,processors, and the like can be implemented by hardware such as anintegrated circuit or the like. Alternatively, those components,functions, and the like can be implemented by software as well. In thelatter case, a processor can interpret and execute the programs designedto serve those functions. The programs, associated data tables, files,and the like can be stored on a stationary storage device such as amemory, a hard disk, and a solid state drive (SSD) or on a portablestorage medium such as an integrated circuit card (ICC), an SD card, anda DVD.

Further note that the control lines and information lines shown aboverepresent only those lines necessary to illustrate the presentinvention, not necessarily representing all the lines required as aproduct. Thus, it can be assumed that almost all the components are infact interconnected.

1. A fan module for taking in and discharging air, comprising: a statorlocated on an upstream side with respect to airflow; and an axial flowfan located on a downstream side with respect to the airflow; wherein,when the fan module is viewed from a rotational-axial direction of theaxial flow fan, the stator includes a stator vane trailing edge and theaxial flow fan includes a rotor vane leading edge, the trailing edge andthe leading edge each having two points of intersection with twoconcentric circles having different diameters, and wherein a straightline connecting the two points of intersection on the trailing edge anda straight line connecting the two points of intersection on the leadingedge are configured such that if, on one of the two concentric circles,one point of intersection on the trailing edge is superimposed on thepoint of intersection on the leading edge, on the other of the twoconcentric circles, the other point of intersection on the trailing edgeis not coincident with the other point of intersection on the leadingedge.
 2. The fan module according to claim 1, wherein the rotor vane hasa tilt direction opposite to that of the stator vane.
 3. The fan moduleaccording to claim 1, wherein the stator vane constituting part of thestator is configured to be warped like a U-shape.
 4. The fan moduleaccording to claim 3, wherein the stator vane applies a reversepre-swirl to the rotor vane.
 5. The fan module according to claim 1,wherein a second stator is disposed on the downstream side of the axialflow fan.
 6. The fan module according to claim 5, wherein a trailingedge of a stator vane constituting part of the second stator disposed onthe downstream side of the axial flow fan is located at a positiveposition with respect to a position of a leading edge of the stator vanein a rotational direction of the axial flow fan.
 7. The fan moduleaccording to claim 1, wherein an interval between adjacent stator vanesconstituting part of the stator is smaller than a width of a finger. 8.The fan module according to claim 1, wherein the axial flow fan and thestator constituting the fan module are integrated with each other. 9.The fan module according to claim 1, wherein a plurality of the fanmodules are combined in series or in parallel.
 10. Server equipment inwhich the fan module according to claim 1 is mounted.